A pancreatic B-cell depolarizes in response to glucose externally applied. The glucose-induced depolarization provokes a spike-train followed by a sudden repolarization which interrupts the spike-train. The mechanism of this sudden repolarization has not been elucidated. The present study was aimed at the elucidation of the mechanism of the sudden repolarization terminating the spike-burst activity.Isolated mouse pancreatic islets were used throughout the experiments. Intracellular Ca^<2+> concentration and pH were fluorometrically monitored. The amount of ATP in cells was calculated from the count of photons emitted from luciferase-luciferin mixed with cell homogenate. Electrical activity of B-cell was recorded by using a microelectrode of very high resistance. The results obtained are as follows; 1) After switching the external glucose concentration from 2.8mM to 11.1mM, intracellular Ca^<2+> elevated with an onset of spike activity, and returned to the initial resting level on the c
… Moreessation of the electrical activity. 2) In the presence of 11.1mM glucose, the removal of external Ca^<2+> caused a fall of the intracellular Ca^<2+> concentration, while the spike-train continued during the entire period of Ca^<2+>-free conditions. Intracellular pH was not affected by the removal of external Ca^<2+>.3) In a low Na+ solution containing 11.1mM glucose, the intracellular Ca^<2+> concentration remained at the high level. Under the same condition, the electrical activity continued without being interrupted by a repolarization. Intracellular pH slightly decreased when external Na^+ was replaced by either Li, choline, or N-methyl-D-glucamine, while the replacement of NaCl with Tris-HCl induced an alkalinization of cytosol. 4) The ATP content increased when external Ca^<2+> was removed. Similarly, any procedures lowering the external Na^+ concentration to 25mM caused an increase in the ATP content. 5) Amiloride also brought about an increase of the ATP content. In contrast to the effect of amiloride, monensin which caused a repolarization lowered the intracellular ATP level.These results indicate that the sudden repolarization terminating the spike-burst activity is due to a fall of the ATP level which is a consequence of an increase in the ATP consumption by the elevated Na^+/K^+-pump activity. Less